fix(deploy): add shell: bash for bash-specific syntax in deploy-k8s.yaml

${SHA:0:7} substring expansion is bash-specific and fails in sh.
Adding explicit shell: bash to both steps, matching the fix already
applied to build-push.yaml.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/deploy-k8s.yaml

@@ -35,6 +35,7 @@ jobs:
     if: gitea.ref == 'refs/heads/main'
     steps:
       - name: Install yq
+        shell: bash
         run: |
           set -euo pipefail
           ARCH=$(uname -m)
@@ -47,6 +48,7 @@ jobs:
           chmod +x /usr/local/bin/yq
 
       - name: Update image tag in cluster repo
+        shell: bash
         run: |
           set -euo pipefail